development and evaluation of a quick release posterior
TRANSCRIPT
Development and Evaluation of a Quick Release Posterior Strut
Ankle Foot Orthosis
Wentao Li
Thesis submitted to the Faculty of Engineering
in partial fulfillment of the requirements for the degree of
MASTER OF APPLIED SCIENCE
in Mechanical Engineering
University of Ottawa
Ottawa, Ontario
October 2020
© Wentao Li, Ottawa, Canada, 2020
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Abstract
Ankle foot orthosis (AFO) stiffness affects ankle range of motion but can also provide
energy storage and return to improve mobility. To perform multiple activities during the day, a
person may want to change their AFO stiffness to meet their activity’s demand. Carrying multiple
AFO and changing the AFO is inconvenient and could discourage users from engaging in multiple
activities. This thesis developed a new quick-release mechanism (QRM) that allows users to easily
change posterior strut elements to change AFO stiffness. The QRM attaches to the AFO and requires
no tools to operate. The new QRM includes a quick-release key, weight-bearing pin, receptacle
anchor, and immobilization pin. A prototype was modelled with SolidWorks and simulated with
SolidWorks Simulation. The QRM was designed to have no mechanical failure during intense
activities such as downhill walking and running. Unlike a solid screw connection, the QRM needed
an additional part to eliminate unsecured motion related to clearance between the quick release key
and receptacle anchor. Mechanical test results and measurement data demonstrated no deformation
on each part after mechanical testing. User testing revealed that, although the quick release
mechanism can be locked or unlocked rapidly, the person’s posture when operating can facilitate
strut swapping. A learning effect occurred by repeated practice. The Quick Release AFO (QRAFO)
prototype verified the manufacturing feasibility of the QRAFO design. Overall, the novel quick
release AFO improved strut swapping time without sacrificing device strength.
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Table of Contents
Abstract ................................................................................................................................................. ii
Table of Contents ................................................................................................................................. iii
Table of Figures .................................................................................................................................. vii
List of Tables ....................................................................................................................................... ix
Definitions ............................................................................................................................................. x
Abbreviations ....................................................................................................................................... xi
Acknowledgments ............................................................................................................................... xii
Chapter 1: Introduction ......................................................................................................................... 1
1.1 Rationale............................................................................................................................. 1
1.2 Objectives ........................................................................................................................... 2
1.3 Thesis contributions ........................................................................................................... 2
1.4 Thesis outline ..................................................................................................................... 3
Chapter 2: Literature Review ................................................................................................................ 4
2.1 Gait cycle............................................................................................................................ 4
2.2 Ankle kinematics and kinetics during gait ......................................................................... 5
2.2.1 Range of motion ...................................................................................................... 5
2.2.2 Moment and power .................................................................................................. 6
2.3 Ankle foot orthosis ............................................................................................................. 7
2.3.1 Traditional passive AFO .......................................................................................... 8
2.3.2 Posterior leaf spring AFO ........................................................................................ 9
2.3.3 Carbon fibre AFO .................................................................................................... 9
2.4 Posterior strut AFO .......................................................................................................... 10
2.4.1 Intrepid dynamic exoskeletal orthosis (IDEO) ...................................................... 11
2.4.2 Dynamic Strut AFO ............................................................................................... 11
2.4.3 Posterior Dynamic Element AFO .......................................................................... 12
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2.5 Variable stiffness AFO ..................................................................................................... 13
2.5.1 Series elastic actuation active AFO ....................................................................... 13
2.5.2 Magnetorheological fluid brake AFO .................................................................... 13
2.5.3 Active artificial muscle AFO ................................................................................. 14
2.6 Summary .......................................................................................................................... 15
Chapter 3: Design Criteria .................................................................................................................. 16
3.1 Response time .................................................................................................................. 16
3.2 Stiffness ............................................................................................................................ 16
3.3 Weight .............................................................................................................................. 16
3.4 Device lifespan ................................................................................................................. 17
3.5 AFO joint strength ............................................................................................................ 17
3.6 Design criteria summary .................................................................................................. 18
Chapter 4: Quick Release Posterior Strut Ankle Foot Orthosis Design .............................................. 19
4.1 Quick release mechanism design criteria ......................................................................... 19
4.2 Quick release mechanism model ...................................................................................... 20
4.2.1 Quarter turn fastener model ................................................................................... 20
4.2.2 Sliding locking model ............................................................................................ 20
4.2.3 Quarter-turn cam lock model ................................................................................. 21
4.2.4 Concept Evaluation ................................................................................................ 22
4.3 QRAFO modeling ............................................................................................................ 24
4.3.1 QRAFO CAD prototype ........................................................................................ 24
4.3.2 Quick release mechanism ...................................................................................... 25
4.4 FEA mechanical analysis ................................................................................................. 27
4.4.1 Assumptions .......................................................................................................... 27
4.4.2 Fatigue analysis formulation ................................................................................. 28
4.4.3 Running load analysis ............................................................................................ 31
4.4.4 Downhill walking load analysis............................................................................. 32
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4.5 Summary .......................................................................................................................... 36
Chapter 5: Mechanical Evaluation ...................................................................................................... 37
5.1 Testing methodologies ..................................................................................................... 37
5.1.1 Running load testing protocol ................................................................................ 37
5.1.2 Downhill walking load testing protocol ................................................................ 38
5.1.3 Data processing ...................................................................................................... 39
5.1.4 Dimension evaluation ............................................................................................ 41
5.2 Mechanical evaluation results .......................................................................................... 41
5.2.1 Running load.......................................................................................................... 41
5.2.2 Downhill walking load ......................................................................................... 42
5.2.3 Dimension measurements ...................................................................................... 42
5.3 Summary .......................................................................................................................... 43
Chapter 6: Quick Release Evaluation.................................................................................................. 44
6.1 Test AFO .......................................................................................................................... 44
6.2 Methods ............................................................................................................................ 45
6.3 Results .............................................................................................................................. 46
6.4 Strut swap behaviour test ................................................................................................. 47
6.4.1 Methods ................................................................................................................. 47
6.4.2 Results ................................................................................................................... 48
6.5 Summary .......................................................................................................................... 50
Chapter 7: QRAFO Prototype ............................................................................................................. 51
7.1 Carbon fibre lamination.................................................................................................... 51
7.1.1 Lamination components ........................................................................................ 51
7.1.2 Strut modification .................................................................................................. 53
7.1.3 Lamination procedures .......................................................................................... 54
7.2 QRAFO Prototype ............................................................................................................ 57
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Chapter 8: Conclusions and Future Work ........................................................................................... 58
8.1 Summary and conclusions ................................................................................................ 58
8.2 Future work ...................................................................................................................... 59
8.2.1 Mechanical strength for highly active users .......................................................... 59
8.2.2 Further QRAFO functional tests ............................................................................ 60
References ........................................................................................................................................... 61
Appendix A: Technical drawings of designed QRM components ...................................................... 67
Appendix B: Purchased parts specifications ....................................................................................... 76
Appendix C: Activities circuit list ....................................................................................................... 77
Appendix D: Quick release AFO questionnaire .................................................................................. 79
Appendix E: Certificate of ethics approval ......................................................................................... 82
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Table of Figures
Figure 2-1 Three anatomical planes (sagittal, frontal, transverse) and six directions (left, right,
anterior, posterior, superior, inferior). Adapted from [3]. ..................................................................... 4
Figure 2-2 Gait cycle and phases. Adapted from [4]. ........................................................................... 5
Figure 2-3 Ankle motion in three anatomical planes (Adapted from [2]). ............................................ 5
Figure 2-4 Ankle dorsiflexion and plantarflexion during one gait cycle. Adapted from [5]. ............... 6
Figure 2-5 Sagittal ankle moment (Nm/kg, left) and power (J/kg, right). Adapted from [6]. ............... 6
Figure 2-6 (a) Thermoplastic rigid AFO, (b) flexor joint articulated AFO. Adapted from [17] ........... 8
Figure 2-7 Posterior leaf-spring AFO. Adapted from [20]. .................................................................. 9
Figure 2-8 Carbon fibre strut AFO (left), Össur AFO Light (right). Adapted from [22], [24]. .......... 10
Figure 2-9 IDEO orthosis .................................................................................................................... 11
Figure 2-10 Dynamic Strut AFO ......................................................................................................... 12
Figure 2-11 Posterior Dynamic Element AFO .................................................................................... 12
Figure 2-12 SEA adaptive controlled AAFO (Adapted from [36]). ................................................... 13
Figure 2-13 Original i-AFO prototype (left), second generation (middle), third generation (right). .. 14
Figure 2-14 Pneumatic actuated AFO. Adapted from [46]. ................................................................ 14
Figure 4-1 Quarter turn fastener mechanism. ...................................................................................... 20
Figure 4-2 Sliding lock mechanism .................................................................................................... 21
Figure 4-3 Quarter-turn cam lock model............................................................................................. 22
Figure 4-4 Quarter-turn cam lock locking operation by turning the octagon cam .............................. 22
Figure 4-5 Quick-release AFO prototype and its components ............................................................ 24
Figure 4-6 Quick release mechanism .................................................................................................. 25
Figure 4-7 Foldable bail design quick release key (left), immobilization pin (middle), and quick
release receptacle (right) ..................................................................................................................... 26
Figure 4-8 Anchor isometric view from top (left); Anchor isometric view from bottom (right) ........ 26
Figure 4-9 SolidWorks simulation result of Ti-pin under walking load ............................................. 30
Figure 4-10 Solidworks simulation result of anchor under walking load ........................................... 30
Figure 4-11 Load and fixture position on meshed QRM equivalent to running load ......................... 32
Figure 4-12 Solidworks simulation of Ti-pin and anchor under running load .................................... 32
Figure 4-13 Free body diagram of strut during downhill walking, where W is user body weight, Mf is
the reaction moment. 80% body weight is exerted on cuff and 20% body weight on the sole. .......... 33
Figure 4-14 Load and fixture position on meshed QRM with downhill walking impact load ........... 34
Figure 4-15 Solidworks simulation of Ti-pin and anchor under downhill walking load .................... 35
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Figure 5-1 (a) Testing setup for downhill walking impact test; (b) anchor fitting in “orthosis” with
press fit; (c) quick release key and Ti-pin epoxied with “strut” .......................................................... 38
Figure 5-2 Testing setup for downhill walking test ............................................................................ 39
Figure 5-3 Running load test (trial 1) unprocessed data, showing force-displacement relationship... 40
Figure 5-4 Spectrum of measured forces and the Butterworth filter with running load (left) and
downhill walking load (right) .............................................................................................................. 40
Figure 5-5 Force-displacement curve plotted from the running load data .......................................... 41
Figure 5-6 Force-displacement curve from 20-degree downhill walking load test ............................. 42
Figure 6-1 3D printed AFO with quick release mechanism (left) and screw-anchor mechanism (right)
............................................................................................................................................................. 44
Figure 6-2 3D printing AFO and cuff components ............................................................................. 45
Figure 6-3 An example of the starting of strut removing (left) and starting strut attaching (right) .... 46
Figure 6-4 Range and mean of total swap time of QRM .................................................................... 47
Figure 6-5 Range and mean of total swap time of screw anchor mechanism ..................................... 47
Figure 6-6 Time to swap strut with QRM ........................................................................................... 48
Figure 6-7 Time to swap strut with screw anchor mechanism ............................................................ 49
Figure 7-1 Quick release components ................................................................................................. 51
Figure 7-2 Lamination tools ................................................................................................................ 52
Figure 7-3 Strut modification (transparent view) ; front view (left); side view (right) ....................... 54
Figure 7-4 Assembly of QRM, dummy plates and strut ..................................................................... 54
Figure 7-5 Introducers to cover anchor cavities (except slot in the middle). ...................................... 55
Figure 7-6 Carbon fibre fabric laminating over the anchor................................................................. 55
Figure 7-7 Lamination packed by press pad ....................................................................................... 56
Figure 7-8 Dummy plate pressed lamination, fixed by fixer introducer ............................................. 56
Figure 7-9 The QRAFO prototype ...................................................................................................... 57
Figure A-1. Technical drawing of anchor ........................................................................................... 67
Figure A-2. Technical drawing of immobilization pin ....................................................................... 68
Figure A-3. Technical drawing of 3D printing shank ......................................................................... 69
Figure A-4. Technical drawing of 3D printing sole ............................................................................ 70
Figure A-5. Technical drawing of 3D printing snap shell ................................................................... 71
Figure A-6. Technical drawing of strut dummy plate ......................................................................... 72
Figure A-7. Technical drawing of strut lamination dummy plate and press pad ................................ 73
Figure A-8. Technical drawing of receptacle introducer .................................................................... 74
Figure A-9. Technical drawing of fixer introducer ............................................................................. 75
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List of Tables
Table 2-1 Gait function and ankle motion for each phase of normal walking [3] ................................ 7
Table 3-1 MSAFO design criteria ....................................................................................................... 18
Table 4-1 QRM design criteria ........................................................................................................... 19
Table 4-2 Concept selection criteria.................................................................................................... 23
Table 4-3 Parts, materials, and sources for the quick release mechanism .......................................... 27
Table 4-4 Maximum stress and safety factors of the QRM parts ........................................................ 35
Table 5-1 Means and standard deviations (mm) of the original dimensions and dimensions after
running load and downhill walking load tests ..................................................................................... 42
Table 6-1 Average time for removal and attachment for QRM and screw-anchor, in groups of 10
trials (standard deviation in brackets) ................................................................................................. 50
Table 7-1 Lamination tools specifications .......................................................................................... 52
Table 8-1 QRAFO design criteria and achievement list ..................................................................... 59
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Definitions
Anterior To the front of the body
Centre of mass Point representing a body’s mean position of mass
Distal Away from the rest of the body
Dorsiflexion Foot rotation towards the knee
Eversion Foot rotation away from the midline of the body
External moment Moment applied from outside the body
Gait cycle Interval between any repetitive events of walking
Frontal plane Divides the body into front and back (aka, coronal plane)
Ground reaction force Reaction force from the ground applied to the foot
Internal moment Moment generated by muscles and/or ligaments
Internal rotation Rotation about long axis, with anterior surface moving medially
Inversion Foot rotation towards the midline of the body
Kinematics Joint or body segment movements
Kinetics Forces and moments that produce movement
Lamination A laminated structure of carbon fibre fabrics
Lateral Away from the midline of the body
Medial Towards the midline of the body
Orthosis Assistive device that supports, aligns, prevents, or corrects deformities
or improves movement
Plantarflexion Foot rotation away from the knee
Posterior To the back of the body
Proximal Towards the rest of the body
Power Rate at which work is done or energy is expended
Sagittal plane Divides the body intro right and left
Stance Gait cycle phase when foot contacts the support surface
Step Foot strike of one extremity to foot strike of opposite extremity
Stride Foot strike of one extremity to next foot strike of same extremity
Swing Gait cycle phase without foot contact on the support surface
Transverse plane Divides the body into upper and lower
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Abbreviations
AFO Ankle-foot orthosis
AAFO Active ankle-foot orthosis
CFAFO Carbon fibre ankle-foot orthosis
COM Centre of mass
FEA Finite element analysis
GRF Ground reaction force
IDEO Intrepid Dynamic Exoskeleton Orthosis
IM-pin Immobilization pin
MR Magnetorheological
MSAFO Multiple stiffness ankle-foot orthosis
PCC Pearson correlation coefficients
PDEAFO Posterior dynamic element ankle-foot orthosis
PLSAFO Posterior leaf spring ankle-foot orthosis
QRAFO Quick release ankle-foot orthosis
QRM Quick release mechanism
QTCL Quarter-turn cam lock
QTF Quarter-turn fastener
ROM Range of motion
SEA Series elastic actuator
SLM Sliding locking mechanism
Ti-pin Titanium pin
TOHRC The Ottawa Hospital Rehabilitation Centre
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Acknowledgments
First of all, I would like to thank my two supervisors, Dr. Natalie Baddour & Dr. Edward
Lemaire for all of their guidance, support, and encouragement throughout my research.
A thank you also goes out to the following individuals:
Staff of Rehabilitation Technology Lab
Staff of Prothetics and Orthotics Department
Staff of Brunsfield Center
Finally, thank you to my family and friends.
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Chapter 1: Introduction
Ankle foot orthoses (AFO) are mobility enhancement devices that assist people with gait
disabilities. AFO functions evolved from assisting foot drop to providing gait control, thereby
enhancing walking and standing ability. One recent advancement in AFO design uses a posterior
strut element that can store and return energy during movement. An off-loading cuff reduces weight
bearing on the foot and ankle, thereby allowing users with ankle disabilities to engage in more
intense activities such as running and uneven road walking. Orthotists can customize a device by
selecting strut stiffness to correspond to the user’s activity level and body weight. However, a stiffer
device limits the ability to perform some activities that require ankle range of motion beyond the
strut material deformation, such as casual walking and driving. Currently, there is no available AFO
that allows a person to switch AFO stiffness to match different activities, other than carrying multiple
devices and then changing to a completely different AFO.
In this thesis, a new quick-release ankle-foot orthosis (QRAFO) was proposed to provide a
solution that allows users to change device stiffness to better accommodate a range of physical
activities. A preliminary FEA simulation on design safety was performed, followed by mechanical
evaluations to verify mechanical performance on running loads and downhill walking loads. Lastly, a
quick release mechanism (QRM) functional test was designed to assess the strut swap time with
comparison of strut swap time with a screw-anchor connection used in the Posterior Dynamic
Element Ankle-foot Orthosis (PDEAFO, Figure 1-1).
Figure 1-1 Posterior Dynamic Element Ankle-foot Orthosis. Adapted from [1]
1.1 Rationale
Users participating in different activities require different AFO stiffness. Current posterior
strut AFO designs, including the Intrepid Dynamic Exoskeleton Orthosis (IDEO) and the Posterior
Dynamic Element Ankle-foot Orthosis (PDEAFO), allow an orthotist to select a strut with
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appropriate stiffness, based on user activity level and body weight. Since the strut is connected to the
foot and shank parts by lock-tightened screws, users cannot easily swap struts during the day.
Although the modularized design helps users to select the most appropriate stiffness for daily use, the
need to change device stiffness between activities has not been addressed to date. For example, a user
still needs to remove their device while driving to allow for more ankle motion.
A device with a changeable stiffness would assist the user to better engage in different
activities. Section 2.5 reviews many active AFO approaches to change stiffness during activities.
Most active AFOs only consider stiffness control during a walking gait.
The current modularized design of a posterior strut AFO can be utilized and improved to
achieve multiple stiffnesses among multiple needs, by redesigning the ankle joint connection such
that it enables fast swapping.
1.2 Objectives
The objectives of this thesis are:
1. Design a quick release mechanism that replaces the current PDEAFO anchor system.
2. Evaluate quick release mechanism mechanical properties:
a. Overall strength under running load and downhill walking load.
b. Evaluate connection strength under running and downhill walking loads.
3. Evaluate quick-release mechanism efficiency for reducing strut-swap time.
4. Verify the manufacturing feasibility of QRAFO.
1.3 Thesis contributions
The principal contribution of the thesis was creating and validating a QRAFO that provides
appropriate device stiffness, thereby providing better energy storage and return during different
activities for PDEAFO users.
Specific thesis contributions are:
1. Designing a viable quick release mechanism for a posterior strut AFO.
2. Demonstrating that the new design can accommodate running and downhill walking
loads.
3. Evaluating the quick release mechanism function and determining that posterior struts on
a 3D printed prototype can be swapped in less than 10 seconds.
4. Creating a complete carbon fibre QRAFO, thereby verifying the fabrication process that
will be used by orthotists and orthotic technicians.
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1.4 Thesis outline
This thesis is divided into eight chapters. Chapter 2 is a literature review covering ankle
function during gait, state of the art in ankle-foot orthoses, and AFO effects on gait. Chapter 3
presents the QRAFO design criteria. Chapter 4 introduces the quick-release mechanism design;
including, design concept development, QRAFO prototype, formulation to avoid component fatigue,
FEA evaluation on strength under fatigue, peak running load, and peak downhill walking load.
Chapter 5 presents the quick release mechanism mechanical evaluation with running and downhill
walking load. Chapter 6 performs functional analysis of a 3D printed QRAFO with able bodied
participants. Chapter 7 concludes the fabrication process of the QRAFO and validates the process
with a QRAFO prototype. Chapter 8 concludes the thesis and outlines future work on the QRAFO.
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Chapter 2: Literature Review
This chapter reviews biological ankle-foot mechanics and ankle-foot orthoses, to better
determine design criteria and gain insight regarding ankle-foot orthosis effects on gait.
2.1 Gait cycle
The ankle joint complex is located between the lower leg and the foot and forms the kinetic
linkage allowing interaction between the lower limb and ground [2]. The ankle plays a vital role in
weight-bearing during gait while also providing stability [3]. Twenty-six individual bones with
thirty-three joints function simultaneously to control the ankle motion on three anatomical planes
(Figure 2-1).
Figure 2-1 Three anatomical planes (sagittal, frontal, transverse) and six directions (left, right,
anterior, posterior, superior, inferior). Adapted from [4].
A walking gait cycle can be defined from one-foot landing to the same foot contacting the
ground again (i.e., stride), with this cycle divided into stance and swing phases (Figure 2-2). Stance
phase is the period with foot-ground contact, with five subphases: initial contact, loading response,
mid-stance, terminal stance, pre-swing. The swing phase has three sub-phases: initial swing, mid-
swing, terminal swing.
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Figure 2-2 Gait cycle and phases. Adapted from [5].
2.2 Ankle kinematics and kinetics during gait
Three key pairs of ankle movements occur on three anatomical planes, plantarflexion and
dorsiflexion in the sagittal plane, abduction and adduction in the transverse plane, and inversion and
eversion in the frontal plane (Figure 2-3, Table 2-1) [3].
Figure 2-3 Ankle motion in three anatomical planes (Adapted from [3]).
2.2.1 Range of motion
Ankle range of motion (ROM) is an important kinematic parameter during gait. Ankle
motion occurs primarily in the sagittal plane, with plantarflexion and dorsiflexion. Maximum sagittal
plane ROM ranges from 65 to 75°, with 40-55° plantarflexion and 10-20° dorsiflexion [3]. Frontal
plane ROM ranges from 23 of inversion to 12 of eversion [3].
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Sagittal ROM during daily activities is much smaller than the full range, with approximately
30° for walking [3]. Ankle sagittal plane ROM consists of controlled plantarflexion at initial contact
to maximum dorsiflexion during terminal stance, up to 15º, rapid plantarflexing to a peak of 18º at
toe-off, and controlled dorsiflexion during swing, for a total ROM of approximately 33º (Figure 2-4).
Figure 2-4 Ankle dorsiflexion and plantarflexion during one gait cycle. Adapted from [6].
2.2.2 Moment and power
Figure 2-5 shows sagittal plane ankle moment and power for one gait cycle. Small
dorsiflexion moments and powers occur after initial contact due to heel strike [4]. Ankle
plantarflexion moments increase continuously throughout midstance and into late terminal stance,
when foot push-off begins with plantarflexion moment decreasing rapidly until toe-off. The largest
moment occurs at terminal stance phase (approximately 1.6 Nm/kg) [7]. Mild dorsiflexion moments
occurs throughout swing phase to control foot angle and maintain foot-ground clearance [4], [7]. Gait
cycle power curves show energy peak requirements at terminal stance when push-off happens. This
rapid push-off is the largest power generation phase of all lower limb joints [7].
Figure 2-5 Sagittal ankle moment (Nm/kg, left) and power (J/kg, right). Adapted from [7].
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Table 2-1 Gait function and ankle motion for each phase of normal walking [4]
Subphase % Gait Ankle motion Function
Stance
Initial
contact 0-10 Neutral
Dorsiflexors are active to resist plantarflexion
to avoid foot slap, and plantarflexion begins
Loading
response 10-12
Plantarflexion
and subsequent
dorsiflexion
Dorsiflexors control ankle rotation to smooth
plantarflexion to foot flat and then assist
dorsiflexion to midstance
Mid-stance 12-32 Dorsiflexion
Dorsiflexor moments assist ankle rotation to
mid-stance and then eccentric plantarflexor
moments control shank rotation over the foot
Terminal
stance 32-50
Dorsiflexion and
subsequent
plantarflexion
As the heel rises, the toes remain flat on the
ground and ankle continues rotation to peak
dorsiflexion, plantarflexors maintain the ankle
angle as the knee begins to flex, ankle rotates
into plantarflexion in late terminal stance
Pre-swing 50-60 Plantarflexion
Plantarflexors rapidly plantarflex the ankle,
producing a forward horizontal reaction force
to advance the body
Swing
Initial
swing 60-77 Dorsiflexion
Foot leaves the ground with maximum
plantarflexion and dorsiflexors lift toes and
hold the foot in dorsiflexion, maintaining foot-
ground clearance
Mid-swing 77-86 Neutral
Dorsiflexors continue to contract mildly to
maintain a neutral position for toe-ground
clearance
Terminal
swing 86-100 Neutral
Dorsiflexor contractions increase to hold the
ankle in position, in anticipation of the greater
forces needed during loading response
2.3 Ankle foot orthosis
Ankle foot orthoses (AFO) are assistive devices that control ankle motion and provide
stability for people with limb weakness or spasticity. AFO differ by materials, joint connection,
geometry, and power condition [8]. Generally, AFO can be classified as passive, semi-active, and
active. Semi-active and active AFO have actuators, power sources, and control systems, with direct
or indirect motion control. Although semi-active and active AFO can adapt ankle rotation control
during gait, passive AFO are the most popular device due to the lower cost, smaller size, lighter
weight, and many other benefits [9].
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2.3.1 Traditional passive AFO
Passive AFO is the most common AFO and addresses abnormal gait due to ankle
dysfunction. Passive AFO are usually worn by people with lower limb paralysis (stroke, etc.) [10],
neuromuscular disease resulting in lower limb weakness (foot drop, etc.), and spasticity that holds the
foot and ankle in biomechanically poor positions and limits movement (cerebral palsy, etc.) [11].
Two classic passive AFOs are the articulated AFO and non-articulated AFO (also called
rigid AFO). Articulated AFOs are usually hinge connected with a defined motion range. Non-
articulated AFO is usually a piece of material [10], or several materials, connected rigidly.
Non-articulated AFOs are traditionally fabricated from thermoplastics to allow for easy
modification, although carbon fibre devices are becoming common as prefabricated devices and for
user’s some special needs. The footplate trimline, proximal border, and proximal closure strap can be
adjusted to modify focal force locations, changing the stabilizing bending moments [12]. Frontal
plane motion is limited via localizing medial-lateral AFO forces, proximal and distal to the malleoli.
For increased stability against foot inversion/eversion, the anteroposterior and footplate trimlines can
be extended [12]. Articulated AFO can resist plantarflexion during swing phase to prevent foot drop
and provide some free ankle motion during stance.
Both rigid or articulated AFO can appropriately control ankle motion, thereby increasing
dorsiflexion at initial contact and swing phase for people with ankle dysfunction [13]–[17]. More
dorsiflexion during stance phase occurs when wearing a hinged AFO than a rigid AFO [17], [18].
Ankle plantarflexion moment is significantly increased in loading response and ankle dorsiflexion
moment is decreased in terminal stance with articulated AFO, compared with the rigid AFO [17].
(a) (b)
Figure 2-6 (a) Thermoplastic rigid AFO, (b) flexor joint articulated AFO. Adapted from [19]
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2.3.2 Posterior leaf spring AFO
The posterior leaf spring (PLS) AFO features shallow medial and lateral trimlines, [12], [20],
[21], thereby providing more flexibility in the sagittal plane. The traditional PLSAFO is fabricated
from thermoplastic (Figure 2-7).
Figure 2-7 Posterior leaf-spring AFO. Adapted from [22].
From initial contact to early loading response, the posterior leaf decelerates ankle rotation
and minimizes foot slap. In mid-stance, the leaf spring permits controlled dorsiflexion through large
material deformation, providing smooth tibia advancement until late stance [12]. During terminal
stance, as plantar flexor begins, energy stored in the leaf spring releases and assists push-off. The
posterior leaf spring resists plantarflexion, holding the foot in slight dorsiflexion, during swing phase.
A small amount of ankle rotation can occur during swing, dependent on thermoplastic thickness and
posterior strut trimlines [12].
2.3.3 Carbon fibre AFO
Although some PLSAFO designs can assist plantarflexion and allow dorsiflexion, push-off
assistance is minimum [23]. Therefore, PLSAFO designs were adapted to incorporate carbon fibre
materials to provide enhanced energy storage from loading response through midstance and energy
release from terminal stance to preswing [12], [24], [25]
The carbon fibre spring is typically L-shaped, with the base attached to the plantar surface of
the footplate and the upright attached to the posterior surface of the proximal cuff [12]. Compared
with thermoplastic AFO, the carbon fibre strut’s increased stiffness requires more force to deform
and returns greater force as the AFO returns to its original shape. The orthotist selects carbon fibre
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spring stiffness based on the person’s weight and activity level. Carbon fibre AFO (CFAFO) can also
be prefabricated devices, such as Össur AFO Light (Figure 2-8).
Figure 2-8 Carbon fibre strut AFO (left), Össur AFO Light (right). Adapted from [24], [26].
Carbon fibre AFO typically enhance gait control and improve biomechanical outcomes [24],
[25], [27]–[29]. Compared with traditional PLSAFO, the CFAFO significantly increased ankle
ROM, ankle angular velocity, and power generation at pre-swing [24], [25], [28]. Improved push-off
was achieved by AFO energy storage through loading response and midstance, resulting in a forward
push of the shank during terminal stance, thereby increased push-off [28]. Bartonek et al. reported
increased positive work at the ankle when wearing a carbon fibre AFO, compared with regular
thermoplastic AFO (from 0.06 to 0.09 J/kg). These results were still much lower than able-bodied
gait (0.25 J/kg) [29].
2.4 Posterior strut AFO
People suffering from limb salvage injuries may be unable to perform intense activities with
a typical plastic AFO due to insufficient energy storage and return [23]. This class of AFO are worn
by people with excessive ankle and foot pain that requires foot unloaded during stance and people
with volumetric muscle loss that requires energy storage and return during push off (military
personnel who have under gone limb salvage, etc.) [23], [30].
Though CFAFO designs improve gait and provide more energy return during push-off, the
energy return was insufficient for high-active activities such as running and jumping [29], [30].
Posterior strut AFO implements a rigid posterior strut as an individual functional component,
providing better energy storage and return, facilitating return to high-intensity activities [30], [31].
11
2.4.1 Intrepid dynamic exoskeletal orthosis (IDEO)
The Intrepid Dynamic Exoskeletal Orthosis (IDEO), developed by the Center for the Intrepid
(San Antonio, TX), is a custom, energy-storing device that supports and protects people with lower
extremity trauma limb salvage injuries [23]. The IDEO is crafted with three carbon fibre components:
ground reaction cuff, mounted posterior strut, and footplate (Figure 2-9). The ground reaction cuff is
a circumferential support fashioned in the style of a patellar-tendon-bearing prosthesis, located at the
proximal part of the leg with a posterior attachment to the proximal end of the carbon fibre strut [30].
The ground reaction cuff provides off-loading to alleviate ankle pain. The posterior strut can deform
to provide energy storage and return. A cushioned heel absorbs shock during loading response. IDEO
advanced modular design allows struts changes as strength and motion ability change, and can be
easier to don and doff [23], [30].
Jeanne et al. compared the IDEO with a regular CFAFO and PLSAFO. The IDEO
significantly improved performance on five training activities: four-square step test, sit-to-stand test,
stair ascent, self-selected speed walking on level terrain, self-selected speed rocky terrain, and 40-
yard dash [30], [32]. The off-loading cuff reduced ankle pain [31], [32].
Figure 2-9 IDEO orthosis. Adapted from [23].
2.4.2 Dynamic Strut AFO
The Dynamic Strut AFO [33] by Coyote Design (Figure 2-10) combines an energy return
strut with custom thermoformed AFO. The combination of thermoplastic and energy return strut
provides dorsiflexion or plantarflexion stabilization with energy return for more active people,
12
thereby covering a wider activity range during daily use. Strut selection is based on user weight and
activity level.
Figure 2-10 Dynamic Strut AFO. Adapted from [33].
2.4.3 Posterior Dynamic Element AFO
The Posterior Dynamic Element AFO (Figure 2-11) [1] is another posterior strut AFO that is
entirely fabricated from carbon fibre. AFO strut stiffness can be selected to match user activities. The
PDE AFO introduced an anchor system by laminating a pre-threaded metal plate within the carbon
fibre matrix, thereby facilitating strut adjustment. Similar to the IDEO, PDE AFO provides high
energy return and off-loads body weight during intense activities.
Figure 2-11 Posterior Dynamic Element AFO. Adapted from [1].
13
2.5 Variable stiffness AFO
2.5.1 Series elastic actuation active AFO
A variable-impedance active ankle-foot orthosis (AAFO, Figure 2-12) was proposed by
Joaquin et al. [34] to treat drop foot. A thermoplastic articulated AFO was the main body and a series
elastic actuator (SEA) connected the proximal cuff and sole. The SEA was located on the posterior
sagittal plane that controlled ankle sagittal plane motion [35]. This 2.6kg device controlled ankle
rotatory stiffness, thereby providing an adaptive control at each gait phase to enhance walking.
Figure 2-12 SEA adaptive controlled AAFO (Adapted from [36]).
The control policy prevented foot slap from heel strike to midstance. During late stance, the
controller minimized impedance to not impede power plantarflexion. In swing phase, impedance was
controlled to maintain foot dorsiflexion, preventing toe drag.
2.5.2 Magnetorheological fluid brake AFO
Magnetorheological (MR) fluid brakes have been researched over the last two decades in
rehabilitation devices. This type of brake utilizes a liquid state that responds to magnetic fields [37].
Varying the magnetic field provides controllable braking forces, which contribute to variable
dampening at the ankle, thereby enable variable resistance at different gait phase. MR fluid brake
devices have been reported for ankle-foot orthosis joints [38], [39], knee brace joints [37], and
prosthetic joints [41]. Compared with conventional motors, MR fluid brakes have better force control
and better energy efficiency [42].
Kikuchi et al. developed a novel variable dampening AFO utilizing MR fluid brake and
spring (i-AFO) [39], [43], [44]. The latest i-AFO (Figure 2-13) demonstrated a high torque-to-weight
14
ratio with 10 Nm maximum output torque on a 237g brake. While preventing foot drop, the MR
brake damping effect also controlled ankle rotation during loading response. Generally, the MR
brake improved gait patterns for people with abnormal gait [45].
Figure 2-13 Original i-AFO prototype (left), second generation (middle), third generation (right).
2.5.3 Active artificial muscle AFO
Ferris et al. developed a pneumatic artificial muscle AFO (Figure 2-14) to provide ankle
torque to assist gait [46]. An active pneumatic tube connected the AFO cuff (anterior) and AFO sole
(posterior). An external pump supported the 1.7 kg weight device. Peak dorsiflexion moment was
20.7 Nm and peak plantarflexion moment was 50.7 Nm, 36% of plantarflexor power and 123% of
dorsiflexor power [46].
Figure 2-14 Pneumatic actuated AFO. Adapted from [46].
15
2.6 Summary
An ankle-foot orthosis can improve walking mechanics and safety, thereby improving
quality of life. Traditional plastic AFO are widely used because of their low cost, while properly
addressing drop-foot and severe ankle instability issues [9]. However, the thermoplastic leaf spring
AFO limits ankle movement to achieve these functional benefits [10]. Articulated AFO compensate
for this rigid AFO limitation by allowing dorsiflexion during stance [17]. The PLSAFO design limits
ankle movement but does provide some dorsiflexion during stance by larger material deformation
and superior energy return [47]. Lower than able-bodied energy storage and return during pushoff
remains a limitation for both articulated and PLSAFO [23], [30].
Different CFAFO designs can provide a lighter and lower profile device, provide better
energy storage and return during terminal stance and pre-swing, or improve knee and ankle stability
[27]. The energy storage and return CFAFO design can help people return to more intense activities.
Unlike plastic AFO, the CFAFO is hard to adjust (pressure points on limb, leaf spring stiffness, etc.)
once the resin has cured [48]. With thermoplastic AFO, orthotists typically adjust the shape during
the fitting process for optimal function and comfort
IDEO researchers built a modularized device that allowed physicians to select strut stiffness
to match user activity levels [23] and stiffer struts can be selected than regular CFAFO. An off-
loading option was also added to the IDEO cuff to reduce pain when performing intense activities
[23], addressing active user’s needs when returning to their previous activities.
Though the IDEO and posterior strut AFO allow individuals to engage in a broader range of
activities, users cannot effectively perform all daily activities with one strut stiffness. Active devices
that provide better stiffness control were proposed. MIT’s SEA controlled AFO was bulky and heavy
compared with other AFO options, which made the SEA device difficult for daily use. The
pneumatic artificial muscle AFO provided large force during push-off; however, the need for an
external pump made the device not portable. MR fluid breaks provided variable damping control
during initial contact, but minimum assistance during push-off [39], [44] and the devices were
heavier than other AFO designs.
To better address return-to-activities needs, either a powerful and portable active AFO or a
strut switchable posterior AFO may be considered.
16
Chapter 3: Design Criteria
This chapter presents multiple stiffness AFO (MSAFO) functionality and design criteria. The
goal of a MSAFO is to allow an AFO user to change AFO stiffness to improve ankle control
performance across daily activities. A quick release AFO (QRAFO) is a MSAFO approach where a
posterior strut can be rapidly swapped, thereby changing AFO stiffness.
3.1 Response time
Two types of response times should be considered: material response time and stiffness
changing time. Material response time is important and must be faster than the loading response
phase. Winter reported average natural cadence for level ground walking to be 105.3 steps/min [49],
which implies that the average stride time starting from initial contact to the next foot contact is 1.14
seconds. Weight acceptance task time is approximately 0-12% of the gait cycle [50], which would
correspond to approximately 0.14 seconds for natural cadence walking and 0.17 seconds for slow
cadence. The delay for the control, including material reaction time and control policy time, should
be less than 0.01 seconds.
A person can spend 30 seconds putting on a shoe [51]. With this as a basis, changing
stiffness by manually swapping struts should take less than 30 seconds for end-user acceptance.
3.2 Stiffness
A multiple stiffness AFO should provide appropriate ankle stiffness during gait,
demonstrated by improved walking range of motion (ROM) and ankle moments. Able-bodied ankle
ROM during walking is 10-20° dorsiflexion and 10-15° plantarflexion [3]. The maximum ankle
moment in the sagittal plane is 1.6 to 2.0 Nm/kg during walking [52]. For people who lack
plantarflexion strength, plantarflexion moments are generated by AFO material deformation energy
storage and return. The maximum desired moment from the MSAFO is at least 20% of the maximum
ankle moment (0.32 Nm/kg) [52].
3.3 Weight
Device weight is an important design factor for assistive technology. An active AFO has a
weight range from 0.86 to 2.6 kg [52], with an average weight of 1.55 kg. For end-user acceptance,
the MSAFO should weigh less than 1.5 kg.
17
The device user’s body weight is important for ankle biomechanics and AFO failure. The
MSAFO must withstand the force exerted during loading response and other weight-bearing periods.
Walpole et al. estimated that an average American weighs 80.7 kg [53]. The U.S. Department of
health and human services [54] reported that the average male over 20 years old, between 2011 and
2014, weighed 88.8 kilograms. The 90th percentile of US male weight is 113.3 kg. Meanwhile, the
average body mass of US females in the same criterion is 74.7 kg and the 90th percentile of the same
criterion is 104.0 kg. Therefore, considering that users may carry backpacks, MSAFO should
withstand daily use by a 120 kg person.
3.4 Device lifespan
Daily activities can lead to AFO material fatigue. MSAFO life should be a balance between
product cost and device endurance. Consumers are suggested to replace their orthosis every two or
three years [55]; therefore, the MSAFO should function appropriately for at least three years of
normal usage. A review paper indicated that an average healthy adult takes 4000 to 18000 steps per
day, and that 10000 steps/day is a common goal for healthy adults [56]. Therefore, the target life for
MSAFO under walking load is approximately 107 cycles.
3.5 AFO joint strength
MSAFO will be used for most daily activities, from light activities such as sitting to intense
activities such as running. The orthosis must withstand impacts from loading response during intense
activities such as running and steep downhill walking. Maximum ground reaction forces (GRF) can
reach or surpass three times body weight during running at 5 m/s on level ground [57]–[59]. A 16.5
to 24-degree slope is considered as a strong slope [60]. With this as a basis, MSAFO should be able
to support user walking at a 20-degree slope. The peak vertical ground reaction force while
descending a 20-degree ramp can be 1.2 times body weight [61].
For highly active users, the AFO can provide offloading at the orthosis cuff, based on user
need [1], [23]. The MSAFO design should have the capacity of offloading up to 80 percent body
weight during running or downhill walking.
18
3.6 Design criteria summary
MSAFO design criteria are summarized in Table 3-1.
Table 3-1 MSAFO design criteria
Objective Criteria
Function Stiffness changed automatically or manually
User weight range Maximum 120 kg
AFO weight Maximum 1500 g
Range of motion -15 to 20 degrees
Peak moment generated by AFO 0.32 Nm/kg
AFO endurance 107 gait cycles
19
Chapter 4: Quick Release Posterior Strut Ankle Foot
Orthosis Design
A quick-release approach is proposed to enable posterior-strut AFO users to efficiently swap
struts to change AFO stiffness and better accommodate multiple activities during daily living,
thereby providing a MSAFO. The quick release AFO (QRAFO) design is based on the PDEAFO
concept (Chapter 2.4.3). To enable quick release and swapping, a novel quick-release mechanism
(QRM) was developed.
This chapter presents the process of designing the quick-release posterior strut ankle-foot
orthosis; including, how the QRM design relates to the design criteria, three design ideas, and a
scoring scheme based on desired functions to select the QRM design approach. A prototype QRAFO
is described and simulation and mechanical analyses on the QRM are reported (fatigue analysis, level
ground running strength analysis, downhill walking strength analysis). Safety factors to material
yielding are calculated.
4.1 Quick release mechanism design criteria
In a posterior strut AFO, the strut is securely bolted to the proximal and distal AFO sections,
requiring tools and time to change struts. To make the device portable, the QRM must be operated by
hand without tools and be integrated into the AFO components. Users are expected to swap struts
within 30 seconds (Table 4-1).
The QRAFO must work robustly under the design criteria weight, without failure. The QRM
should function appropriately for at least three years under normal activities without material failure
or mechanism problems.
Table 4-1 QRM design criteria
Item Criteria
Connection with orthosis Affixed
QRM width Equal or less than the strut width
Release method Tool-free
Steps to swap strut Maximum 4 steps
Time to swap strut Maximum 30 seconds
Weight Maximum 50 grams
20
The QRM will be located between the energy return strut and orthosis. A compact size not
exceeding the strut width would reduce the chance of the QRM being damaged during use or the user
being hurt by contact with the QRM. Therefore, the QRM width should not exceed the strut width.
QRM weight is important for user acceptance and reducing the energy burden for “carrying
the AFO” during the day. Therefore, the QRM should be as light as possible while not sacrificing
strength. The QRM design target is less than 50 grams.
4.2 Quick release mechanism model
4.2.1 Quarter turn fastener model
Figure 4-1 shows a quarter-turn fastener (QTF) quick-release mechanism model concept.
Two quarter-turn keys, affixed on the strut, are used to lock the entire mechanism. One weight-
bearing pin bears the body-weight load. Corresponding receptacles for the quarter-turn keys can be
affixed on an anchor, which is molded into the orthosis.
Figure 4-1 Quarter turn fastener mechanism.
The QRM locks by aligning the strut and orthosis, pushing the male assembly into the female
assembly, and turning the quarter-turn key.
4.2.2 Sliding locking model
A sliding locking mechanism (SLM, Figure 4-2) uses a latch pin as the locking mechanism.
The latch pin is attached to a trapezoidal male carrier and fits another female anchor with a
trapezoidal groove. The carrier side surface and the inner anchor surface are in contact and prevent
21
sagittal plane motion. During gait, sagittal plane forces are taken by the carrier and anchor, thereby
reducing force on the latch pin. Three holes on the anchor allow the user to adjust AFO cuff height.
The pin only takes shear load when multidirectional forces and moments exist. A spring between the
carrier and latch pin pulls the latch into the anchor hole. The spring ends affix to the carrier and latch
pin. The anchor is attached on the orthosis posterior surface and the carrier is affixed on the posterior
strut. The lock procedures are: 1) align the strut and orthosis, 2) slide the carrier on the strut into the
anchor on the orthosis, 3) align hole and latch pin and release the latch.
Figure 4-2 Sliding lock mechanism
4.2.3 Quarter-turn cam lock model
Figure 4-3 shows the quarter-turn cam lock (QTCL) model. One anchor with a pin hole will
be on the orthosis. Other components will attach to the strut. The locking mechanism will be limited
in a carrier affixed to the strut. The locking mechanism includes the octagon cam, pin board, and
spring. The pushing pin board lies on the carrier’s bearing so that motion is limited to one direction.
The cam pushes the pin board and locks the anchor with the carrier by turning the cam 90 degrees.
The spring pushes the pin board back to the unlock position by turning the cam for another 90
degrees (Figure 4-4). The flat surface stabilizes the mechanism by providing a large contact area
between pin board and cam.
22
Figure 4-3 Quarter-turn cam lock model.
Turn 90 degrees
Turn 90 degrees
Figure 4-4 Quarter-turn cam lock locking operation by turning the octagon cam
Users lock the mechanism by aligning the strut and orthosis, pushing the male assembly into
the female assembly, and turning the cam.
4.2.4 Concept Evaluation
The quarter-turn fastener model is less bulky since its male components can be affixed
directed on the strut. The turning operation is limited by the turning directions, with the user turning
the key only in one direction to lock the QRM. This mechanism takes two steps to lock and requires
sagittal plane alignment. The number of component types added to the orthosis is four. For
23
manufacturing, the anchor needs one machine tool, either CNC milling machine or regular milling
machine. The pin, quarter-turn key, and receptacle can be purchased.
Security is highlighted with the sliding lock mechanism. The trapezoidal shape fit between
the carrier and anchor reduced the risk of being pulling out. The locking operation is one step, as
simple as releasing the latch pin. However, two alignment processes are required before releasing the
latch pin, including aligning the carrier with the anchor groove and aligning the latch pin with the
anchor holes. The number of component types is four, and two of these can be purchased off-the-
shelf. The carrier and anchor need to be machined with a milling machine. More manufacturing time
should be spent on the slope surface of the carrier and anchor.
The quarter-turn cam lock model can be easily operated by turning 90 degrees in either
direction. This mechanism takes two steps to lock and needs frontal plane alignment. The number of
component types added to the orthosis is five, while the handle and springs can be purchased. For
manufacturing, the pin board and carrier need more than two machine tools, such as mill machine
and lathe, to manufacture the QRM.
Table 4-2, the quarter-turn fastener model has more positive aspects than the other two
models. Therefore, the QR AFO was prototyped using the quarter-turn fastener mechanism.
Table 4-2 Concept selection criteria
Locking Effort
Steps to lock Lock motion limits Steps to Align Alignment planes
QTF 2 Turn one direction 1 Sagittal
SLM 3 None 2 Frontal and Sagittal
QTCL 2 None 1 Sagittal
Best Models QTF, QTCL SLM, QTCL QTF, QTCL QTF, QTCL
Efforts on acquiring parts
# part types # purchasable parts # machine jobs # machine tools
QTF 4 3 1 1
SLM 4 2 2 1
QTCL 6 2 4 2
Best Models QTF, SLM QTF QTF QTF, SLM
Bulkiness and Security
Required carriers or anchors Motion prevention
QTF Only the anchor Motion between pin and anchor
SLM Both carriers and anchors Motion between carrier and anchor
QTCL Both carriers and anchors Motion between carrier and anchor
Best Models QTF SLM, QTCL
24
4.3 QRAFO modeling
4.3.1 QRAFO CAD prototype
The QRAFO model was divided into three sections: top orthosis, carbon fibre strut system,
and bottom orthosis (Figure 4-5). The quick-release mechanism consisted of a quick-release key,
receptacle, and titanium pin. The receptacle was epoxied with the anchor and they were affixed in the
orthosis and covered with carbon fibre. The quick-release components (quarter turn fastener,
receptacle) were purchased from Skybolt Aeromotive Corporation (ZG2600R2, SK213-2, Cloc®,
Appendix B). The quarter-turn fastener and the titanium pin (Ti-pin) were epoxied with the strut.
Grade 5 titanium (Ti-6V-4Al) was selected to improve strength. An immobilization pin (IM-pin)
located between the quarter-turn fastener and the Ti-pin prevented unnecessary plantar plane motion.
An adjustment panel was located between the strut and quarter-turn fastener.
Part Number Name
1 Anchor
2 Thickness compensation plate
3 Immobilization pin
4 Quick-release key
5 Titanium pin
6 Orthosis sole
7 Energy return strut
8 Cam lock receptacle
9 Orthosis cuff
Figure 4-5 Quick-release AFO prototype and its components in exploded view
25
4.3.2 Quick release mechanism
The quick-release mechanism consists of a Ti-pin, quick release key, receptacle, anchor, IM-
pin, and an adjustment panel (Figure 4-6). The receptacle was epoxied with the anchor, which was
molded into the orthosis. The Ti-pin took the role of weight-bearing, by contacting the anchor first
when load was applied, to protect the quarter-turn fastener. Machined grade 5 Ti-pins that had
enough strength to withstand landing impact were purchased. Pin length was longer than the quarter-
turn fastener’s stud length so that pin alignment assists stud alignment. Using only one receptacle
makes the quick-release mechanism more compact. An adjustment panel between the fastener and
strut minimized axial motion between the strut and quarter-turn fastener. Clearance between the
quick release key and receptacle caused rotation around the Ti-pin, between the strut and orthosis.
The IM-pin was crafted to prevent this rotation.
Figure 4-6 Quick release mechanism
The quarter-turn fastener consisted of the stud, sleeve, and spring. A foldable bail handle that
can fold into a flat position was selected (Figure 4-7). A spring between the sleeve and key shaped
metal provided push out force that helped the key remain stable when locked with the receptacle. The
quick-release key had a foldable bail so that the key was able to remain low profile. The
immobilization pin was constructed from a cylindrical and another rectangular part. The cylindrical
end was epoxied with the strut and the rectangular end fit the anchor slot.
26
Figure 4-7 Foldable bail design quick release key (left), immobilization pin (middle), and quick
release receptacle (right)
The hollowed anchor design (Figure 4-8) reduced weight while guaranteeing strength. The
extruded cylinder and Ti-pin were clearance fit, thereby enabling smooth lock and unlock movement.
The diamond shape groove fit the receptacle. The receptacle and anchor were press-fit and epoxied to
ensure the receptacle was fixed securely. A slot at anchor center fit the IM pin.
Figure 4-8 Anchor isometric view from top (left); Anchor isometric view from bottom (right)
The receptacle was adjustable, with a thread cam shape screw (Figure 4-8). The thread cam
could change position and then maintain the position with a leaf spring. The quick-release key
travelled through the groove, inside the screw, and locked. The adjustable design provided a larger
range of clamped panel thicknesses. The strut swapping steps were: 1) align the pin to the anchor, on
orthosis calf and foot shells; 2) push the strut into the orthosis; 3) turn quarter-turn fastener to lock
the device. Model materials are listed in Table 4-3.
27
Table 4-3 Parts, materials, and sources for the quick release mechanism
Part Material Source
Anchor Aluminum 6061 Machined from raw material
Pin Titanium Alloy Ti-6Al-4V Allied Titanium Inc.
Quarter turn fastener Aluminum 6061 Skybolt Aeromotive Corp.
Receptacle Aluminum 6061 Skybolt Aeromotive Corp.
IM-pin Acetal Machined from raw material
4.4 FEA mechanical analysis
Mechanical analysis is important as a preliminary determination of appropriate material and
geometric decisions. Material failure of the QRM or AFO can hurt the end user. For example, if the
energy return strut breaks or the quick release key detaches during movement, improper foot-ground
contact that could produce a stumble or fall. QRM failure or deformation could disable the quick
release mechanism, lead to the strut being stuck in the AFO or the user not being able to reattach the
strut into the AFO, leaving the person to unsafely walk without their AFO.
The AFO design in this thesis followed regular clinical practice for PDEAFO. Therefore, the
AFO strength is not discussed in the thesis and FEA modelling focussed on QRM components.
4.4.1 Assumptions
QRM design assumptions are:
QRM can be attached to an offloading orthosis. Eighty-percent weight offloading from the foot
was considered in the design.
QRM can withstand a person walking on a 20-degree ramp without material failure.
QRM can withstand loads when running at 5 m/s without material failure.
User inertia when moving was not considered.
Friction between the quick release male and female components was not considered.
The device will be used mostly in moderate climate conditions.
Adhesive material around the QRM will not fail.
Orthosis and strut deformations were negligible for calculation.
For calculations, 10 ms-2 was considered as gravity acceleration.
28
4.4.2 Level ground fatigue analysis formulation
QRAFO was designed for long periods of daily use. Fatigue failure occurs when an object is
subjected to time-variable loading. Commonly, the fatigue strength is well below the ultimate static
strength [62], [63]. Fatigue strength when the specimen reaches infinite life length is called the
endurance limit. While the stated endurance limit of grade 5 titanium is 510 MPa, the actual
endurance limit is affected by component loading conditions. Modifying factors are defined and used
to account for long-period repeated loading using Marin equation [63]
𝑘 = 𝑘𝑎𝑘𝑏𝑘𝑐𝑘𝑑𝑘𝑒𝑘𝑓 (4-1)
where k is the modifying factor, affected by six different subfactors: surface modification (ka), size
(kb), loading (kc), temperature (kd), reliability (ke), and miscellaneous effect (kf).
The actual endurance limit modified by Marin factors is
𝑆𝑒 = 𝑘𝑆𝑒′ (4-2)
where 𝑆𝑒 denotes the actual endurance limit and 𝑆𝑒′ is the ideal endurance limit.
Factors were estimated for pre-design phase. The surface modification factor is affected by
the quality of the part surface. Lipson and Noll presented an experience equation for the surface
modification factor [63]
𝑘𝑎 = 𝑎(𝑆𝑢𝑡)𝑏 (4-3)
where Sut is the ultimate tensile strength, and a and b are regression factors.
The size effect should be considered and expressed by the size factor. Mischke et al. [64]
derived equations for size factor based on 133 sets of data points. The small circular rod equation is
𝑘𝑏 = (𝑑
7.62)
−0.107
= 1.24𝑑−0.107 2.79 ≤ 𝑑 ≤ 51 𝑚𝑚 (4-4)
where d is the diameter of the Titanium pin and 𝑘𝑏 is the size factor.
Fatigue tests illustrate the difference between three types of loading [65]. This difference can
be compensated by a loading factor, 𝑘𝑐, which is given by
𝑘𝑐 = {1
0.850.59
𝑏𝑒𝑛𝑑𝑖𝑛𝑔
𝑎𝑥𝑖𝑎𝑙 𝐿𝑜𝑎𝑑𝑡𝑜𝑟𝑠𝑖𝑜𝑛
(4-5)
Temperature affects the material properties, becoming a consideration when the temperature
is higher than 449°C [62]. The QRAFO is assumed to work at room temperature, for which the
temperature factor equals one.
29
The standard deviation of endurance strength is less than 8 percent. The reliability factor can
be written as
𝑘𝑒 = 1 − 0.08𝑧𝑎 (4-6)
where 𝑧𝑎 is the transformation variate to reliability factor 𝑘𝑒.
The miscellaneous-effect factor is mutually affected by corrosion, electrolytic plating, etc.
The QRAFO design did not consider these factors.
Walking generates fluctuating stresses among the QRM component. Walking can be
regarded as a cyclic load with the same mathematical patterns such as the mean, amplitude, period
length. A modified Goodman equation is introduced to describe the relationship between the mean
and load amplitude while the life of the parts is at the boundary of infinity.
𝜎𝑎
𝑆𝑒+
𝜎𝑚
𝑆𝑢𝑡= 1 (4-7)
where 𝜎𝑎 is the amplitude component of fluctuating stress, and 𝜎𝑚 is the midrange component.
Modified Goodman equation determines the actual fatigue safety factor. The safety factor to
infinite life is defined and applied to the equation
𝜎𝑎
𝑆𝑒+
𝜎𝑚
𝑆𝑢𝑡=
1
𝑛
(4-8)
where n indicates the safety factor regarding infinite life.
The design was based on calculations with 80% percent body weight offloaded by the AFO
cuff. Research found that PTBAFO off-loading effects decreased by time, with body weight
offloading decreasing to 54.9% after two weeks and to 43.7% after long term use [66]. The QRAFO
design covered more than 90% percent of the body weight range in the USA population [54]. The
titanium weight bearing pin strength in the QRAFO design had more than double the strength of the
two steel bolts used in the commercially available PDEAFO. Therefore, a desired safety factor of one
is sufficient for the analyses in this thesis (i.e., in practice the steel bolts are sufficient to safely secure
a strut to an AFO).
Figure 4-9 Ground reaction forces normalized by body mass for one step while walking on level
ground. Normal force, solid line; shear force, dashed line; standard deviations, dotted lines [61].
30
The maximum ground reaction force during walking on level ground equals bodyweight.
(Figure 4-12) [61].
Maximum stress was calculated by SolidWorks simulation (Figure 4-10). Shear force was
considered in the simulation. The quick release key and receptacle took no load due to the clearance
between these parts. The calculation combines equations (4-2) and (4-8). Since the Modified
Goodman safety factor was 5.09, the Ti-pin will not have material failure caused by fatigue.
Figure 4-10 SolidWorks simulation result of Ti-pin under maximum walking load
Aluminum alloys usually do not exhibit a distinct endurance limit. The experimental fatigue
strength of aluminum for 107 cycles is approximately 117 MPa [67]. Considering the stress
concentration factor, the anchor simulation is shown in Figure 4-11.
Figure 4-11 Solidworks simulation result of anchor under walking load
The Modified Goodman safety factor is 1.37 for the anchor. Both Ti-pin and anchor show a
low chance of failure due to fatigue.
31
4.4.3 Level ground running load analysis
The QRM must support large impact forces when the user performs intense activities. Failure
to absorb impact on the components can transfer the energy to the user and cause injury. Two intense
conditions were applied to the design, level running and walking on a 20-degree descending hill.
Kenneth et. al. [57] found that the maximum ground reaction force during running (5 m/s)
can reach three times body weight (Figure 4-12). Maximum load occurred around mid-stance, where
the ankle maintains a neutral position. Therefore, the force exerted on the QRM was hypothetically
along the strut’s long axis. Shear force was considered between the QRM and orthosis when running
on level ground.
Figure 4-12 Vertical ground reaction force-time waveform predicted by model (5 m/s running) [57].
Stress on the Ti-pin can be expressed as,
𝜏 =𝑉
𝐴
(4-9)
where τ is the shear stress in the pin, V is the shear force applied on the pin, and A refers to the cross-
section area.
The selected grade 5 titanium has a yielding strength of 880 MPa. Therefore, the pin should
not fail. A FEA meshed model was built for the simulation (Figure 4-13). Two rigid fixtures were
designed to simulate the QRM assemblage. Uniformly distributed forces were exerted on the end of
the flat bar. The shell holding anchor was set as a global fixture. The flat bar’s side surface could
only deform in the x or z directions. Y-direction motion was restricted to prevent numerical error
accumulation in the y direction. The clearance interfaces, such as interface between Ti-pin and
anchor, interface between flat bar and shell, and interface between flat bar and anchor, were contact
surfaces with no penetration conditions. Other interfaces were bonded.
To simulate the real situation, a nonlinear solver was used to allow contact conditions to
change due the Ti-pin’s slide behavior. Von Mises stress was calculated among all mesh elements.
Figure 4-14 presents the stress distribution through Ti-pin and anchor, with maximum stress noted.
32
Compared with the Ti-pin and anchor yielding strength (880 MPa and 270 MPa), yielding safety
factors were 5.5 for Ti-pin and 1.07 for the anchor.
Figure 4-13 Load and fixture position on meshed QRM equivalent to running load
Figure 4-14 Solidworks simulation of Ti-pin and anchor under running load
4.4.4 Downhill walking load analysis
Biomechanics research suggests that peak vertical ground reaction force while descending a
20-degree ramp is 12 times the body mass (Figure 4-15) [61], producing 1440 N vertical load on the
foot for a 120 kg person.
33
Figure 4-15 Ground reaction forces normalized by body mass for one step while descending a 20-
degree ramp. Normal force, solid line; shear force, dashed line; standard deviations, dotted lines [61].
The strut free-body diagram for a person walking on a 20-degree hill is shown in Figure 4-16.
By assuming body weight is exerted on the quick release joint, the free body diagram when walking
on a 20-degree hill is shown in Figure 4-16. Forces exerting on two different sole locations produced
a moment on the quick release joint, which was compensated by a reaction moment from quick
release mechanism.
Figure 4-16 Free body diagram of strut during downhill walking, where W is user body weight, Mf is
the reaction moment. 80% body weight is exerted on cuff and 20% body weight on the sole.
A bending moment was exerted on the QRM due to the inclined position. Equation (4-10)
calculated the moment on the QRM.
𝑀𝑓 = 0.8𝑊𝐿 sin(20𝑜) (4-10)
where L indicates the strut length, W is the transferred weight to the orthosis, and Mf denotes the
bending moment generated on the QRM.
The distance between two Ti-pins on the strut accounted for the moment. The moment on a
250 mm long strut was 86.7 Nm with 220 mm lever length. The force component along the strut was
34
1080 N and the transverse force perpendicular to the strut was 394 N. The force along the strut
produced a shear stress on the Ti pin. The force perpendicular to the strut produced a bending
moment on the QRM, and also a pulling force on the quick release key.
Figure 4-17 Load and fixture position on meshed QRM with downhill walking impact load
A FEA model was built with a rigid flat bar and rigid shell (Figure 4-17). The distance
between the flat bar’s upper bound and the Ti-pin hole was 220 mm. A 1080 N sagittal plane load
was exerted uniformly on the flat bar’s upper surface. To generate a moment on the QRM, a 394 N
force in the negative x direction was applied on the edge of the flat bar’s upper surface. The rigid
shell was fixed globally. Since the load should cause deformation only in the sagittal plane, flat bar
frontal motion was prohibited so that numerical errors would not diverge. The mesh size of the quick
release components (quick release key, receptacle) and other components were controlled separately.
Small-value curvature-based mesh was applied to the quick release components due to its complex
shape, aiming to provide precise results.
A nonlinear solver was used to calculate Von Mises stress among all mesh elements. Figure
4-18 presents the stress distribution through the Ti-pin and anchor, with maximum stress noted.
Downhill walking results were different from the running load results. Stress on the Ti-pin
shifted to the front under bending moment. Larger stress on the Ti-pin also occurred. The quick
release key stud and receptacle took less stress during bending. Overall, the components were more
vulnerable when an inclined load was applied. Safety factors are listed in Table 4-4.
35
Figure 4-18 Solidworks simulation of Ti-pin and anchor under downhill walking load
Table 4-4 Maximum stress and safety factors of the QRM parts
Quick-release Parts Running Downhill Walking
Max. Stress (MPa) Safety Factor Max. Stress (MPa) Safety Factor
Ti-pin 159.6 5.51 754 1.17
Anchor 257.2 1.05 266 1.02
QR key 26 10.38
QR receptacle 44 6.14
4.4.5 FEA result analysis on Ti pin
The Ti-pin simulation results showed larger stress for downhill walking compared to running.
To verify the relationship, the stress on Ti-pin was estimated. The stress during running is mainly
shear stress ((4-11)).
𝜏 =𝑉
𝐴
(4-11)
Where V is the shear force, A is the area of Ti-pin, and 𝜏 is the shearing stress. Since the
Area of Ti pin is quadratic with the radius, the transformation of shear stress is expressed as equation
(4-12),
36
𝜏 =𝑉
𝜋𝑟2
(4-12)
Since the downhill walking load caused a moment on Ti-pin, the stress on Ti-pin is
dominated by bending stress shown in (4-13).
𝜎 =𝑀𝑟
𝐼
(4-13)
Where 𝜎 is the maximum bending stress under bending moment M, and I is the inertia of Ti-
pin. The inertia is quartic with radius, which transforms equation(4-13) to equation(4-14).
𝜎 =2𝑀
𝜋𝑟3
(4-14)
The denominator of bending stress is smaller than that of shearing. Therefore, the Ti-pin is
more vulnerable with the downhill walking load compared to the running load.
4.5 Summary
The simulation results show that the QRM is safe for level walking, running, and downhill
walking scenarios. The most vulnerable condition was the user walking on a 20-degree descending
hill. Inferring from this result, downhill and stair walking would have higher chances of device
failure due to the bending moments. These results can have biases due to assumptions and numerical
errors. Mechanical tests should be performed under appropriate loading conditions to ensure that the
device can withstand the loads transferred to the device from running or downhill walking.
37
Chapter 5: Mechanical Evaluation
This chapter presents mechanical testing methodologies and results from the quick release
mechanism (QRM). Two tests evaluated device performance with running load and downhill walking
load. Section 5.1 and 5.2 present the test protocol and the results. Section 5.3 discusses the test
results and presents a series of failure analyses.
5.1 Testing methodologies
Mechanical tests were performed with running (2880 N) and downhill walking (1080 N
vertical, 394 N horizontal, 86.7 N/m bending moment) loads. The QRM components should have no
failure, such as plastic deformation or surface damage, under these loads. Connections between
components should remain in the original state after testing.
5.1.1 Running load testing protocol
High strength steel (Grade 4140, cold roll, annealed) was selected as the jig material that
functioned as orthosis and strut. The quick release stud and receptacle, anchor, and Ti-pin
components were separated into two groups: male parts attached to the “strut” and female parts
affixed on the “orthosis”. The “orthosis” was machined and fitted to the anchor and receptacle. The
“strut” was connected with the “orthosis” by the QRM (Figure 5-1).
The tests were performed using an electromechanical testing machine (4482, InstronR,
Norwood, MA) with a 10 kN static load cell (10 N resolution, ISO-376, InstonR, Norwood, MA
[68]). Two fixture positions were available on the machine. The top fixture had a cylindrical shape
with an iron plate beneath. The iron plate’s horizontal surface provided force along the vertical axis.
The bottom fixture had a jaw shape to clamp the specimen.
The load cell provided 2880 N maximum force at a constant speed of 1 mm/min. The steel
strut was clamped on the testing machine. The load cell initial position was manually set to
approximately one millimeter from the iron shell. A smartphone was fixed on a tripod and video
recorded the trials. When the force sensed by the load cell reached 2880 N or the displacement
reached 10 mm, the load cell terminated action and returned to origin position. Ten trials were
collected and analyzed.
38
(a)
(b)
(c)
Figure 5-1 (a) Testing setup for downhill walking impact test; (b) anchor fitting in “orthosis” with
press fit; (c) quick release key and Ti-pin epoxied with “strut”
The Instron machine used Bluehill software to create the test method and record data at
10 Hz. Load cell displacement and force data were saved in comma-separated values (CSV) format.
Video data were collected from the smartphone and saved as MOV format. After testing, the force-
displacement relation was explored by analysing the slope of the curve. Besides, quick release
component dimensions were measured by a calliper with 0.01 mm resolution (Accusize Industrial
Tools, AB11-1106) before and after testing to determine surface damage between Ti pin and
aluminum anchor.
5.1.2 Downhill walking load testing protocol
The downhill walking load test was similar to the running load test since QRM components
were affixed on the same “orthosis” and “strut” and the same testing machine and load cell were
used. However, the top fixture was replaced with a 20-degree triangle hot rolled steel part that
provided force in two directions. The fixture on the bottom (jaw shaped clamp) secured the
specimen.
39
The load cell provided 1080 N maximum force at a constant speed of 1 mm/min. The steel
strut was clamped on the testing machine (Figure 5-2). The load cell’s initial position was manually
set to one millimeter away from the iron shell. A smartphone was fixed on a tripod and recorded the
procedures. Note that the machine can only detect the vertical force and displacement. The load cell
would terminate action and return to origin position if the vertical load reached 1080 N. Ten trials
were collected and analyzed.
Figure 5-2 Testing setup for downhill walking test
5.1.3 Data processing
The load cell started at a different location during each trial. Therefore, the “touching point”
of the data (Figure 5-3), where the load cell touched the specimen, was identified so that the
measured displacement would be equivalent to specimen deformation along the strut. The maximum
measured force before the load cell touching the specimen was below 10 N. The maximum value was
tracked from zero displacement until a 5-sample string larger than 10 N occurred. The first sample
subtracting from this 5-sample string was set as the touching point. Data before the touching point
was discarded.
40
Figure 5-3 Running load test (trial 1) unprocessed data, showing force-displacement relationship
Data collected from the sensor contained noise from the displacement sensor, load cell force
sensor, material surface roughness, etc. Raw data were normalized to 500 points using spline
interpolation, and the spectrum of data was normalized from 0 to 1. Force data were filtered using a
4th order Butterworth filter with normalized cut off frequency of 0.10 πrad/sample (Figure 5-4) to
keep the major part of the spectrum.
Figure 5-4 Spectrum of measured forces and the Butterworth filter with running load (left) and
downhill walking load (right)
After removing noise, the force-displacement curves were analysed. Pearson correlation
coefficients (PCC) for force-displacement curves and slope-displacement relations were calculated to
assess trial similarity.
41
5.1.4 Dimension evaluation
Any displacement caused by deformation and surface damage can lead to the dimension
change after tests. Measurable component dimension changes included Ti-pin diameter, Ti-pin length,
and anchor pin hole diameter. A calliper with 0.01 mm resolution (Accusize Industrial Tools, AB11-
1106) was used. Twenty measurements were made at different locations on each measured
component, before testing, after running load test, and after downhill walking load test. Mean and
standard deviation were calculated after each test.
5.2 Mechanical evaluation results
5.2.1 Running load
Load cell forces monotonically increased in relation to material deformation (Figure 5-5).
The slope of the curve did not decrease, indicating that the material did not reach the yielding point
where plastic deformation occurs.
Figure 5-5 Force-displacement curve plotted from the running load data
PCC between each force-displacement curve was larger than 0.99. PCC close to 1 indicates
that datasets are highly similar. Therefore, the running load tests were repeatable.
42
5.2.2 Downhill walking load
Load cell force monotonically increased with respect to displacement (Figure 5-6); therefore,
the material did not reach the yielding point where plastic deformation occurs. This evidence showed
that components were in their elastic region when the downhill walking load was applied.
Figure 5-6 Force-displacement curve from 20-degree downhill walking load test
PCC between each force-displacement curve was larger than 0.99. Therefore, the downhill
walking load tests were repeatable.
5.2.3 Dimension measurements
Table 5-1 shows mean and standard deviation of the measured dimensions. The mean of the
Ti-pin diameter, Ti-pin length, and anchor hole diameter were within 0.02 mm of their original
dimensions. Since the caliper resolution was 0.01 mm and small human error may have occurred for
caliper placement, these results are within expected measurement error. Therefore, testing did not
produce permanent dimension change on Ti pin, anchor hole. Standard deviations were smaller than
0.02 mm, so measurements along one surface were consistent. Therefore, surfaces were not damaged
due to running and downhill walking loads. Overall, no failure evidence was found from the testing
results.
Table 5-1 Means and standard deviations (mm) of the original dimensions and dimensions after
running load and downhill walking load tests
Before Testing Running Load Downhill Load
Ti-pin diameter (mm) 6.29 (0.01) 6.29 (0.02) 6.28 (0.01)
Ti-pin length (mm) 21.10 (0.01) 21.11 (0.01) 21.09 (0.01)
Anchor hole diameter (mm) 6.37 (0.01) 6.38 (0.01) 6.38 (0.01)
43
5.3 Summary
The mechanical tests evaluated QRM performance on three aspects: plastic deformation,
surface damage, and trial repeatability. The monotonically increasing force-displacement curves
showed that QRM components were in the elastic deformation region within the maximum running
or downhill walking load. Pearson correlation coefficients between trials were close to 1, reflecting
high similarity between trials from the same test. Therefore, the running tests and downhill walking
tests were repeatable. The similar measurement results showed that surface damage did not occur
between Ti pin and anchor. The QRM was verified to have no failures under running and downhill
walking loads.
44
Chapter 6: Quick Release Evaluation
This chapter evaluates QRAFO swapping performance, which is defined as:
• The time to take off and reattach the quick release strut (criterion = less than 30 seconds)
• Strut swapping time using QRAFO is less than the time to swap struts using PDEAFO
Strut swapping time is an important parameter for QRAFO function that affects end-user
acceptance. The time required to remove and reattach a strut was compared between a test AFO with
the QRM and a test AFO with the strut screwed into the AFO (i.e., same attachment method as
PDEAFO). This test received ethics approval from University of Ottawa (Appendix E).
6.1 Test AFO
Two AFO were designed and 3D printed for the quick release timing tests (Figure 6-1). Both
orthoses had identical components (strut, cuff, foot plate) and were manufactured in PLA using an
Ultimaker 2+ printer. One orthosis was configured as a QRAFO, with a QRM bonded to a PLA strut
(250 mm length, 6.35 mm thickness). The second AFO secured a PLA strut to the cuff and foot plate
with 1/4-20 machine screws and 3D printed anchor (screw anchor system). The two AFOs were
modeled in SolidWorks (Appendix A, Figure A-0-3 to Figure A-0-5). The participant wore the 3D
printed AFO on their right foot within their shoe during all tests.
Figure 6-1 3D printed AFO with quick release mechanism (left) and screw-anchor mechanism (right)
45
The cuff was secure on the leg by a strap with a loop-and-hook end (Velcro®). Two parts
formed the cuff: the cuff body and snap shell. The cuff body accommodated the strap and fit the
users calf, and the snap shell press fit the cuff body and fixed the anchor and receptacle to the cuff
(Figure 6-2). The shell inner dimension equaled the anchor dimension (30×50×9.5 mm). The snap
shell was secured on the cuff body with silicone. The quick release key and Ti pin were affixed on
the strut using instant adhesive (Gorilla Glue®). At the back of foot plate, an identical snap shell was
affixed on the foot plate with the anchor and receptacle wrapped. The foot plate was secured on the
foot by a shoe.
Figure 6-2 3D printing AFO and cuff components
6.2 Methods
To record trials, a GoPro was held by the investigator to collect video data at 30 fps, thereby
enabling movement timing and qualitative performance evaluation.
Four able bodied participants were recruited (3 males, 1 female). While sitting, the
participant removed the strut, waited for 2 to 4 seconds, and then reattached the strut. This trial was
repeated 10 times.
The time for strut removal and strut attaching was calculated by determining the start and
end time for each movement from the video. For QRAFO testing, strut removal started when the
participant’s hand touched the QRM and ended when all strut components (strut, quick release key
and Ti pin) were not contacting the QRAFO. Strut attaching started when one of the strut
components touched the AFO and ended when the hand was not touching the QRM (Figure 6-3). For
the screw-anchor connection AFO, removal started when a screwdriver touched the AFO and ended
46
when strut components (strut and screw) were not contacting the AFO. Attaching started when the
strut components touched the AFO and ended when the screwdriver was not contacting the AFO.
Strut swap time is the sum of removal and attaching times.
Figure 6-3 An example of the starting of strut removing (left) and starting strut attaching (right)
Video Editor software from Microsoft Inc was used to identify the starting and ending
frames. The video segments located between starting frames and ending frames were cropped and
exported as mp4 files. Eighty trials were exported into 160 videos (80 attaching and 80 removing,
with QRM and screw anchor mechanism). The video segments durations were then extracted using
MATLAB.
6.3 Results
The mean average swap time of 4 participants with QRM was 25.01 ± 3.66 seconds. Figure
6-4 shows that average swap time with QRM for all participants was within 30 seconds. On average,
participants spent 17.63 ± 3.61 seconds for strut attaching and 7.38 ± 1.79 seconds on strut removing.
Strut alignment to the orthosis was the primary reason why attaching a strut took more time than
removing the strut. The best swap time was 13.83 ± 3.08 seconds, with best attaching time of 8.81 ±
2.17 seconds and best removing time of 4.20 ± 2.31 seconds.
As a comparison, the mean average swap time of 4 participants with screw anchor
mechanism was 60.48 ± 10.88 seconds, 142% larger than swap with QRM. Figure 6-5 shows that
average swap time with the screw anchor mechanism of all participants was more than 30 seconds.
Participants spent 39.94 ± 10.42 seconds averagely on strut attaching, 127% larger than attaching
with QRM, and 20.55 ± 2.25 seconds averagely on strut removal, 178% larger than removal with
47
QRM. The best swap time with screw anchor mechanism was 38.71 ± 3.43 seconds, larger than the
30 seconds criterion.
Figure 6-4 Range and mean of total swap time of QRM
Figure 6-5 Range and mean of total swap time of screw anchor mechanism
6.4 Strut swap behaviour test
Section 6.3 revealed large differences between maximum swap time and minimum swap
time. Participant learning the method to swap strut was the reason for the differences. A strut swap
behaviour test studied the learning effect of strut swap. The behaviour test was performed by a
graduate student (25 years, male).
6.4.1 Methods
To record trials, a smartphone was affixed on a tripod to collect video data at 30 fps, thereby
enabling movement timing and qualitative performance evaluation.
48
The test AFOs were described in Section 6.1. While sitting, the participant removed the strut,
waited for 2 to 4 seconds, and then reattached the strut. This trial was repeated 10 times. After at
least 2 hours, an additional 10 removal and reattachments trials were completed. This was repeated
until a total of 50 trials were collected. This protocol was completed for both QRM and screw-anchor
mechanism.
Video Editor software from Microsoft Inc was used to segment the videos. Fifty trials were
exported into 100 videos (50 attaching and 50 releasing). The video segments durations were then
extracted using MATLAB.
6.4.2 Results
The average time to swap struts with the QRM was 13.85 ± 6.52 seconds and the screw-
anchor was 58.41 ± 11.16 seconds. As the participant learned how to best swap the strut, the best
swap time improved from maximum 35.95 seconds to 6.81 seconds. Figure 6-6 shows the learning
effect since strut swapping time decreased over the first 30 trials. The first ten strut swaps averaged
23.97 seconds and the last ten swaps averaged 8.92 seconds. Standard deviation also improved, with
a standard deviation of the first ten trials of 5.22 seconds and the last ten trials of 1.43 seconds.
Less time was needed to remove the strut than attach the strut. Over the first ten trials, the
average time to attach the strut was 19.70 ± 5.08 seconds, while the last ten trials were 6.24 ± 0.90
seconds (68.3% decrease). The average time to remove the strut, over the first ten trials, was 4.27 ±
0.68 seconds and the last ten trials was 2.68 ± 0.82 seconds (37.2% decrease). QRM swapping time
was less than the 30-second design criteria.
Figure 6-6 Time to swap strut with QRM
49
In comparison, the screw-anchor mechanism averaged 58.41 ± 11.16 seconds to swap
(Figure 6-7). A milder learning effect was seen. The average time to swap the strut for the first ten
trials was 73.39 ± 7.98 seconds, including a mean attaching time of 50.37 ± 4.71 seconds and a mean
removing time of 23.01 ± 6.23 seconds. The average time to swap the strut for the last ten trials was
47.85 seconds, with a mean attaching time of 33.07 seconds and a mean removing time of 14.78
seconds. The time decrease in total swap time between the first ten trials and last ten trials was 34.8%,
including a 34.3% decrease in attaching and 35.8% decrease in removing. Standard deviations were
also larger than the QRM results. The standard deviation of the first ten trials was 7.98 seconds, and
that of the last ten trials was 3.74 seconds. Therefore, more time is required to swap struts when
using an AFO with the screw-anchor mechanism, and the 30-second swapping criterion was not
achieved.
Figure 6-7 Time to swap strut with screw anchor mechanism
The difference between maximum swap time and minimum swap time for the last 10 trials
was distinctively decreased. For strut swap with QRM, maximum swap time for last 10 trials was
10.82 seconds, while the minimum swap time was 6.81 seconds. For strut swap with screw anchor
mechanism, maximum swap time for last 10 trials was 55.00 seconds, while the minimum swap time
was 42.88 seconds.
50
Table 6-1 lists the time to swap strut by mechanism test for each group and movement.
Table 6-1 Average time for removal and attachment for QRM and screw-anchor, in groups of 10
trials (standard deviation in brackets)
QRM Screw-anchor
Strut attaching (1-10) 19.70 (5.08) 50.37 (4.71)
Strut attaching (41-50) 6.24 (0.90) 33.07 (3.48)
Strut removing (1-10) 4.27 (0.68) 23.01 (6.23)
Strut removing (41-50) 2.68 (0.82) 14.78 (1.33)
Strut swap (1-10) 23.97 (5.22) 73.39 (7.98)
Strut swap (41-50) 8.92 (1.43) 47.85 (3.74)
6.5 Summary
This section evaluated QRM performance on swap time. The average swap time of QRM on
the 3D printed QRAFO 24.08 seconds, which satisfies the 30-second target in the design criteria.
Furthermore, the average swap time after practising was 8.92 seconds, which outperformed the 30-
second design criterion. The participant spent 81.36% less time on QRM than the screw-anchor
mechanism used in PEDAFO in the last ten trials. Considering that the QRM can be swapped
without tools, the QRM outperformed screw-anchor mechanism on strut swap.
51
Chapter 7: QRAFO Prototype
This chapter presents the QRAFO fabrication processes and displays the QRAFO prototype.
The QRAFO was fabricated by an orthotist and orthotic technician at The Ottawa Hospital
Rehabilitation Center Prosthetic and Orthotic Department.
7.1 Carbon fibre lamination
As described in section 4.3, the QRM was designed to be bonded with QRAFO components.
The anchors and receptacles were molded in the QRAFO cuff and foot plate, and the quick release
keys, Ti pins, and immobilization pins were bonded on the strut. Carbon fibre fabric was laminated
over the anchor and molded anchor.
7.1.1 Lamination components
Figure 7-1 shows the quick release mechanism components. QRM materials are listed in
section 4.3.2. During lamination, the receptacle thread cam (Figure 7-1) was taken out of the
receptacle. The receptacle was then affixed on the anchor by metal epoxy adhesive (+PLUSeries®).
The strength of epoxy adhesive ranges from 5.17 to 97 MPa [69]. Despite low strength, the epoxy
takes mild resistance force between receptacle and anchor while user accidentally pulling or pushing
the strut. Two locating holes (6-32 thread) were machined in the anchor to guide and position the
strut dummy plates during lamination (Figure 7-2).
Figure 7-1 Quick release components
52
Lamination tools (Figure 7-2) were designed and manufactured to assist carbon fibre fabric
lamination over anchors. Table 7-1 shows the lamination tools specifications, including, names,
materials, manufacturing methods, and functions.
Figure 7-2 Lamination tools
Table 7-1 Lamination tools specifications
Tool Material Manufactured/Purchased Functions during Lamination
Press pads Acrylic Laser-cut using Epilog Laser
Helix 24×18 60 W
While carbon fibre fabric was
laminated over the anchor, the
press pads pressed the fabrics
to pack the fabrics tightly.
Pin hole
introducer PLA Printed by Ultim aker 2+
Before lamination, the pin hole
introducer was placed in the
anchor pin hole. Fabrics were
laminated over anchor through
the pin hole introducer, thereby
leaving the pin hole uncovered.
Fixer
introducer
Steel screws and
PLA
6-32 x 7/8 screws were
purchased. Introducers were
printed by Ultimaker 2+.
Two parts were bonded by
silicone
Before lamination, the fixer
introducer was threaded in the
anchor’s locating hole. Fabrics
were laminated over anchor
through the fixer introducer,
thereby leaving the locating
hole uncovered.
After lamination, the dummy
plate (strut) was placed over
53
the carbon fibre fabrics, and the
fixer introducer was threaded in
anchor threaded hole to lock
the dummy plates with fabrics.
Receptacle
introducer Acetal Machined from raw material
Before lamination, the
receptacle introducer was
threaded in the receptacle.
Fabrics were laminated over
anchor through the receptacle
introducer, thereby leaving the
receptacle thread hole
uncovered.
Dummy plate
(lamination) Acrylic
Laser-cut using Epilog Laser
Helix 24×18 60 W
The lamination dummy plate
was located between anchor
and strut before lamination.
The dummy plate had the same
thickness as lamination.
Dummy plate
(strut) Nylon Machined from raw material
The strut dummy plate was the
dummy for the strut end.
During lamination, the strut
dummy plate was placed over
the lamination. In addition, the
strut dummy plate kept the
lamination surface smooth and
flat during the curing of resin.
7.1.2 Strut modification
The QRAFO prototype utilized the PDEAFO strut. The orthotist chose the strut length for
the user. Quick release key, Ti-pin, and immobilization pin were bonded to the strut. Without
changing the original strut hole diameter, the orthotist used a rotatory tool to machine posts on the
inner hole. In the middle, between pin hole and keyhole, a 5/16-1/8 sink hole was milled to fit the
immobilization pin (Figure 7-3).
54
Figure 7-3 Strut modification (transparent view) ; front view (left); side view (right)
7.1.3 Lamination procedures
1. Bond quick release key, Ti-pin, and immobilization pin with strut.
2. Stack lamination dummy plates on anchors. Then place the assemble strut from step 1 over
dummy plates (Figure 7-4). Turn quick release key to lock anchors and lamination dummy
plates with strut.
Figure 7-4 Assembly of QRM, dummy plates and strut
3. Once assembled, bond the anchor using adhesive (+PLUSeries® Composite) on a target leg cast
model along posterior sagittal plane of the leg model.
4. After the adhesive cured (1 minute), remove the strut, dummy plate, quick release key, threaded
cam and Ti pin.
5. Insert Introducers into anchor pin holes, receptacle threads, and anchor locating holes
(Figure 7-5).
6. Fill the anchor slot with silicone.
55
7. During lamination, the carbon fibre fabrics laminate through introducers, thereby leave the
cavities unlaminated. The cone shape on the top of introducers aided carbon fibre fabrics
laminating over the anchor through Introducer.
Figure 7-5 Introducers to cover anchor cavities (except slot in the middle).
8. Laminate two layers of 45-degree carbon fibre fabric (12 K weight) over the anchor and then
three 0/90 orientation carbon fibre fabric (12 K weight) layers as reinforcement (Figure 7-6).
Spray adhesive over the anchor surface and between each carbon fibre fabric layers during
lamination.
Figure 7-6 Carbon fibre fabric laminating over the anchor
9. Remove fixer introducers.
10. Use press pad to press the lamination and pack the lamination tighter (Figure 7-7). Remove the
press pad after this step.
56
Figure 7-7 Lamination packed by press pad
11. Place strut dummy plates over the anchors and introducers.
12. Tighten strut dummy plates on lamination with fixer introducers (Figure 7-8). Dummy plates
keep the lamination surface flat and smooth as the resin hardens.
13. Laminate the orthosis body over the QRM lamination layup.
14. Seal and fill the entire lamination with resin.
Figure 7-8 Dummy plate pressed lamination, fixed by fixer introducer
15. After the resin hardened, remove the introducers and machine a slot on the QRAFO through
dummy plate slot.
16. Remove strut dummy plate.
17. Assemble the orthosis with strut and quick release male components.
57
7.2 QRAFO Prototype
Figure 7-9 shows the QRAFO prototype. The prototype was fabricated in the Prosthetic and
Orthotic Department in Ottawa Hospital Rehabilitation Centre. The prototype was fitted to the
orthotist who fabricated this QRAFO. The QRAFO prototype was configured with PDE strut (250
mm) and QRM. The Ti pin, quick release key and immobilization pin were bonded with the strut
with glue (+PLUSeries®). A loop-and-hoop strap was mounted on the cuff to secure the cuff on the
calf. The QRAFO weighed 1112 grams and the QRM weighed 30 grams. The prototype validated the
fabrication process of QRAFO.
Figure 7-9 QRAFO prototype
58
Chapter 8: Conclusions and Future Work
8.1 Conclusions and limitations
In this thesis, the quick release strut swapping system of a novel quick-release ankle-foot
orthosis was designed and evaluated to address current PDEAFO limitations. The quick-release
mechanism allows individuals with dorsiflexor/plantarflexor weakness to tune their AFO to their
daily activities; such as, driving, walking, downhill walking, and running. This design was low
profile so that the orthosis will fit beneath normal clothing. The weight added on the strut is minimal,
which motivates users to carry extra struts with different stiffness levels during the day. The QRAFO
was developed in consultation with the staff of the Ottawa Hospital Rehabilitation Centre.
The quick-release mechanism meets the design criteria. The design was lightweight and
compact, which would allow the user to wear the orthosis beneath standard fitting clothing. The
quick-release mechanism components were mostly off-the-shelf, which lowers the device cost. Table
8-1 displays the design criteria and criteria achievement summary.
Mechanical testing revealed that the QRM could bear running and downhill walking loads
for a 120 kg person, with no failure from material or connection. Force-displacement curve analysis
revealed that QRM materials remained in their elastic region under the maximum target loads. The
ten trials showed high repeatability, indicating that the connection was not failing (slipping,
dislocating, etc.) under running and downhill walking loads. Titanium did not to harm the aluminum
anchor’s surface, inferred from low dimension variation between trials.
QRM functional tests demonstrated that the user could swap a strut within 30 seconds. After
learning, a user can swap struts in approximately 10 seconds, which outperforms our design criteria.
As the participant practiced the swapping movement, swap strut time decreased, and with a smaller
time variance.
While the QRAFO met the design requirements for quick release function and strength, the
tests were preliminary for developing a general use device. Mechanical testing proved that the quick
release mechanism had sufficient strength to support loads from intense activities, such as running
and downhill walking, under ideal situations (i.e., occasional intense activities, ideal road and climate
conditions). Further research is needed to verify fatigue performance for long duration intense use,
such as highly active users and athletes. Fatigue testing with higher loads can determine whether the
current material and design has sufficient support.
The climate and road condition criterion are assumed to be moderate. Under extreme cold
weather, the high thermal conductivity of aluminum alloy can be cold to the touch when swapping
struts. Due to the high tolerance of the Ti-pin and anchor, small particles such as sand, that stay
59
inside the anchor can require more push and pull force while swapping struts and may damage the
anchor hole inner surface with prolonged wear. The issue can also occur for muddy road since the
mud can stay in the anchor hole, thereby leading to the difficulty while swapping struts.
Though functional testing verified QRM function, more evaluations are needed to determine
whether the device would motivate the user to swap the strut in their everyday life. A future testing
protocol with AFO users is required to confirm the perceived usefulness and satisfaction on strut
swapping.
Table 8-1 QRAFO design criteria and achievement list
Evaluation
items Design criteria Outcome Summary
AFO weight <1500 grams 1112 grams Achieved
QRM weight <50 grams 30 grams Achieved
Strength
Not breaking during a
120 kg person running
or downhill walking,
considering 80% cuff
off-loading maximum
Mechanical tests on running
load and downhill walking
load showed no failure Achieved
Peak joint
moment
38.4 Nm for 120 kg
person
QRM joint did not fail under
86.7 Nm in downhill walking
test
Achieved
ROM -15-20 degree Free ankle motion when strut
removed
Achieved from
design
Device life Normal walking with
107 cycles
Anchor design has a safety
factor of 1.37, Ti pin has a
safety factor of 5.09
Achieved from
simulation
Swapping time Less than 30 seconds Approximately 10 seconds
after learning Achieved
8.2 Future work
8.2.1 Mechanical strength for highly active users
While the quick release ankle-foot orthosis is promising, improvements can be made in the
future. Simulation of the anchor component revealed that the stress distributed on downhill walking
was close to the strength margin. If the user performs downhill walking or running daily, the anchor
may fail by fatigue due to long term usage. Therefore, the actual life could be shorter than expected.
To not exceed the weight design criteria, high strength aluminum, such as aluminum 2024, may be
considered as an improved version.
60
Mechanical testing proved that the quick release mechanism had enough strength to support
intense activities like running and downhill walking. However, for highly active users who use this
device mostly associate with intense activities (e.g., soldiers on back to duty training, athletics using
the AFO as running support), the anchor could have a risk of fatigue failure. A future mechanical
testing protocol should consider long term intense activities.
8.2.2 QRAFO strut fabrication
In this thesis, a PDEAFO strut was modified to incorporate the QRM. However, machining
carbon fibre can decrease product strength due to carbon fibre damage. Karataş et. al concluded
machined carbon fibre reinforced polymer generally encounters fatigue strength lackness and
composite delamination [70]. Stated in Section 7.1.1, the epoxy connection strength between the Ti-
pin, quick release key, and strut is less than a laminated carbon fibre connection, therefore the
prototype epoxy bonding could lead to failure from impacts or when accidents occur (user falling,
etc.). Therefore, in practice, the QRM components should be laminated into the carbon fiber strut
during manufacturing, thereby providing a quick swap strut that requires no extra machining and
with securely integrated components.
8.2.3 Further QRAFO functional tests
As mentioned in section 8.1, more biomechanical testing should be performed to determine
whether the device motivates users to swap struts during the day. The future testing protocol should
focus on the users perceived usefulness and satisfaction by qualitive measures. An improved testing
protocol should include a large activity range and more participants with lower limb weakness. A
potential solution can be designing an activity list (Appendix C) including light activities and intense
activities, with a questionnaire (Appendix D) to record QRAFO use satisfaction.
61
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Appendix A: Technical drawings of designed QRM
components
Figure A-0-1. Technical drawing of anchor
68
Figure A-0-2. Technical drawing of immobilization pin
69
Figure A-0-3. Technical drawing of 3D printing shank
70
Figure A-0-4. Technical drawing of 3D printing sole
71
Figure A-0-5. Technical drawing of 3D printing snap shell
72
Figure A-0-6. Technical drawing of strut dummy plate
73
Figure A-0-7. Technical drawing of strut lamination dummy plate and press pad
74
Figure A-0-8. Technical drawing of receptacle introducer
75
Figure A-0-9. Technical drawing of fixer introducer
76
Appendix B: Purchased parts specifications
Grade 5 titanium Clevis Pin
Company name: Allied Titanium, Inc.
Trademark True Titanium TM.
Part number: 0020207
Material: Ti-6Al-4V
Finish type: Machined and polished
Yielding strength: 880 MPa
Ultimate strength: 990 Mpa
Quick release key
Company name: Skybolt Aeromotive Co.
Trademark: CLoc
Part number: ZG2600R2
Material: Aluminum 6061
Tensile workload: 200 lbs
Shear workload: 200 lbs
Ultimate strength: 300 lbs plus
Receptacle
Company name: Skybolt Aeromotive Co.
Trademark: CLoc
Part number: SK213-2
Material: Aluminum 6061
Finish type: Machined
Installation option: 3/32 rivet
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Appendix C: Activities circuit list
Following shows an activity circuit [71] to evaluate QRAFO performance in daily activity:
• Start from sitting at a table in uOttawa SITE building (level 1 lobby) with a lower
stiffness strut on the QRAFO.
• Stand up and walk 25m across the lobby to a microwave, open and close the microwave
door, turn and walk back to the seat and sit down.
• Swap QRAFO to the stiff strut.
• Stand still for 30 seconds.
• Pick up a 40-pound backpack from the table.
• Walk through the connection walkway to the uOttawa CBY building level 1 lobby
(55m).
• Walk upstairs to the second floor of CBY and go to the couch area.
• Drop the backpack on a sofa.
• Sit on the bar stool for 30 seconds.
• Go to the spot where a 40-pound dumbbell is on the floor.
• Squat, pick up the dumbbell, and stand up.
• Walk with the dumbbell through a door, around the hallway, and to a conference room
(CBY A212).
• Place the dumbbell on the floor.
• Sit at a table for 30 seconds.
• Remove the strut and sit for 30 seconds.
• Simulate driving for 30 seconds.
• Swap to the lower stiffness strut.
• Walk to CBY level 2 lobby, find a sofa and sit on it.
• Take the strut off, sitting for 30 seconds.
• Stand up, walk to the table, sit on a bar stool for 30 seconds.
• Swap to the lower stiffness strut.
• Walk to the stairs, walk downstairs to CBY level 1 lobby, and walk outside.
• Walk to the uOttawa STEM building over the uphill slope (52m).
• Walk back towards CBY building over the downhill slope, stopping at the level area
between CBY and STEM.
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• If able, swap to the stiff strut without sitting, otherwise sit to swap strut.
• Run 20 meters along the flat area beside STEM.
• Jump 5 times.
• Fast walk counterclockwise along a circle with 5-meter radius.
• Fast walk clockwise along a circle with 5-meter radius.
• Rapidly step left and then back to the right, repeat for 5 times.
• Walk back to SITE building.
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Appendix D: Quick release AFO questionnaire
Participant #: _________________ Date: ______________________
This questionnaire will help evaluate if the quick release ankle-foot orthosis (QR-AFO) meets user needs.
Part 1: User Information
Sex: ___________ Height: _____________(cm/in) Weight: _____________(kg/lb)
Years wearing an AFO: ___________
Part 2: Please rate the following items by circling the appropriate box.
Is the QR-QR-AFO comfortable? All the
Time
Most of the
Time
About Half the
Time Hardly Ever Never
Walking ability when using your QR-
AFO, compared to walking without an
QR-AFO
Much
Improved Improved Same Worse
Much
Worse
QR-AFO appearance Very Good Good Acceptable Poor Very Poor
Effort when using your QR-AFO,
compared to not using a QR-AFO Much Less
Somewhat
Less Same
Somewhat
More
Much
More
How many hours per day do you wear
your QR-AFO?
More than
8 6-8 4-6 2-4 0-2
Where do you use your QR-AFO? Work Only Work,
Home
Work, Home,
Social
Work,
Social
Social
Only
Your QR-AFO’s weight is Very Light Light Not Light or
Heavy Heavy
Very
Heavy
QR-AFO support Very
Secure
Somewhat
Secure
Same as
Without
Orthosis
Somewhat
Insecure
Very
Insecure
QR-AFO support during high intensity
activities (jumping, running, etc.)
Very
Secure
Somewhat
Secure
Same as
Without
Orthosis
Somewhat
Insecure
Very
Insecure
Overall satisfaction with QR-AFO Excellent Above
average Average
Below
Average Poor
Yes No
Does the QR-AFO catch your clothes?
Does the QR-AFO soil your clothes?
Does the QR-AFO make you perspire?
Does the QR-AFO rub your skin?
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Part 3: Please rate the following items for your QR-AFO by placing a mark (x) in the appropriate box. In the
box to the right, please rate the importance of the items for you.
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Part 4: QR-AFO Satisfaction
Please rate your satisfaction with the QR-AFO from 1 to 5, where 1= not satisfied and 5=
very satisfied. You may also write comments to better explain your answer.
Part 5: Comments
1. When would you anticipate swapping the strut during daily living?
2. For the next design iteration, which features do you wish to see on the QR-AFO?
Objectives Score
1. Swapping the strut
Comments:
Carrying the strut
Comments:
2. Overall satisfaction about the quick release mechanism
Comments:
3. Would you use the QR-AFO as your regular device
Comments:
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Appendix E: Certificate of ethics approval
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